This invention relates to a novel thermocouple construction and more specifically relates to a three wire thermocouple which is fixed to a housing adapted to be isolated from the ground of the equipment in which the thermocouple is mounted and wherein the third wire of the thermocouple can be used to ground the thermocouple junction to an instrument ground.
Two wire thermocouples are well known in the art and are commonly used to monitor the temperature of fluids and solids in various applications.
By way of example, two wire thermocouples are commonly used to monitor temperatures in gas cooled dynamoelectric machines of the type shown in U.S. Pat. No. 3,091,710 dated May 28, 1973 in the name of Shartrand et al and are also used for monitoring the temperature of the liquid cooling medium used for cooling stator or rotor windings in applications such as those shown in U.S. Pat No. 3,112,415 dated Nov. 26, 1963 in the name of Bahn et al or U.S. Pat. No. 3,693,036 dated Sept. 19, 1972 in the name of Schmitt.
The standard two wire thermocouple used in equipment of the type described above is normally arranged so that the junction exposed to the fluid whose temperature is measured is also electrically connected to the equipment ground. The equipment ground of dynamoelectric machines and in other applications frequently exhibits considerable noise as compared to the relatively noise-free ground which is available in the monitoring instrumentation and controls to which the thermocouple output is connected. It would be very desiraable to be able to obtain an output signal from a thermocouple which is free of the background noise associated with the ground of the equipment being monitored.